1. Field of the Invention
This invention relates generally to disposable wet-packaged skin cleansing fabrics or cloths formed of paper or other non-woven fibrous webs of the kinds generally known in the art as towelettes, wet-wipes, fem-wipes and the like. It is particularly concerned with the provision of such fabrics which will retain suitable wet tensile strength during storage and use but which can be readily disposed of by flushing in water without danger of clogging the plumbing system.
2. Prior Art
Wet-packaged skin cleansing and refreshing tissues are well known commercially, generally referred to as towelettes, wet-wipes, fem-wipes, and the like. Typical examples of such products are described in U.S. Pat. Nos. 3,057,467; 3,563,371; and 3,398,826. These may comprise an absorbent sheet made of paper, prepared or treated to impart wet strength thereto, having the dimensions of the usual wash cloth and packaged wet in folded condition individually in impervious envelopes or in multiples in closed containers. The liquid employed in pre-moistening the sheet is generally an aqueous alcoholic solution which may further contain a surface-active detergent and a humectant and in some instances also a scenting agent. Instead of individual packaging of such moist sheets, these are often marketed in recloseable containers having any desired convenient numbers of such folded sheets. A typical example of such products particularly designed for use in feminine hygiene, popularly known as "fem-wipes", is disclosed in U.S. Pat. No. 2,999,265.
Certain of the earlier known products suffer from the drawbacks of excessive loss of wet strength on account of being kept moist for even relatively short periods of storage, thereby interfering with their intended use by the consumer. Others of these known products which retain adequate wet strength, cannot be readily disposed of by flushing in water in conventional toilet bowls, since the binders employed in imparting wet strength do not disintegrate sufficiently and thus often cause clogging of the plumbing. In some instances it has been advocated that acidic or alkaline materials respectively be added to the water employed in flushing the used cloths to assist in disintegrating the binder therein, these being selected in accordance with the nature of the resinous binder employed.
Polyvinyl alcohols (PVOH) are well known in commerce for use in textile and paper sizing and coating, as adhesives, binding agents, dispersing/stabilizing agents for emulsions, and the like. These alcohols are generally manufactured by polymerizing vinyl acetate and hydrolyzing the polymer to an alcohol. The marketed grades of polyvinyl alcohol vary in degree of polymerization and degree of hydrolysis. As used herein, "fully hydrolyzed" products are those which have been hydrolyzed to about 95% or higher and up to about 99% by weight. Polyvinyl alcohols having a degree of hydrolysis above 99% are designated as "super hydrolyzed". Films produced from polyvinyl alcohol grades having a degree of hydrolysis above about 95% are resistant to attack by cold water; the extent of water resistance increasing directly with increase in the degree of hydrolysis. Polyvinyl alcohols of lower degree of hydrolysis than the so-called fully hydrolyzed products, such as the "partially hydrolyzed" grades (80-95% by weight hydrolyzed) are almost completely soluble in water at room temperature, while the fully hydrolyzed products have more limited cold water solubility.
Changes in the degree of polymerization affect solution viscosity; i.e. the viscosity of "fully hydrolyzed" and "partially hydrolyzed" products of low viscosity (in 4% aqueous solution at 20.degree. C.) are about 10 cps, medium viscosity are in the range of about the 20-35 cps, and high viscosity are in the range of about 40 cps and above. The viscosity of the aqueous solution of the polyvinyl alcohol is thus an indication of the degree of polymerization.
Surface sizing of paper with aqueous mixtures of polyvinyl alcohol and boric acid is disclosed in U.S. Pat. No. 3,438,808. The boric acid in admixture in the amount of 15% or more of the polyvinyl alcohol and applied in heated condition to the wet, inhibits the extent of penetration of migration of the sizing composition into the paper.
Vinyl acetate copolymer emulsions containing polyvinyl alcohol as a protective colloid are known in the art for use as adhesives, thickeners, coating compositions and the like. Such compositions comprising vinyl acetate-ethylene copolymer emulsions are disclosed, for example, in U.S. Pat. Nos. 3,355,322; 3,708,388; and 3,906,135.
According to U.S. Pat. No. 3,213,051, quick-setting laminating adhesives are prepared by incorporation of boric acid in a polyvinyl acetate emulsion containing polyvinyl alcohol as a protective colloid. To prevent excessive thickening of the emulsion in storage, a viscosity stabilizer and gelation retarding agent is incorporated therein, such as a thiocyanate or urea.
It is also known to employ certain resins and other polymeric materials as binders or coatings on nonwoven fabrics used as toilet-flushable products such as wrappers or outside coverings for diapers and sanitary napkins, surgical dressings and the like, wherein such fabrics need have during their intended use sufficient tensile strength not to disintegrate while in contact with body fluid discharges. Among binders suggested for use in such fabrics are aqueous dispersions of mixtures of acrylic resins and polyvinyl alcohol, as disclosed, for example, in U.S. Pat. No. 3,561,447. In U.S. Pat. No. 3,480,016 it is proposed to employ as a binder for such nonwoven fabrics used for absorbing body discharge, a polymer resin which is (1) stable in neutral or acidic media but which dissolves or degrades in alkaline media or (2) a polymer resin which is stable or insoluble in neutral or alkaline media but soluble or degradable in acidic media; or (3) polymers degraded by oxidizing agents. To dispose of such fabrics after use, the suitable degrading agent is added to the flush water. Among the examples of alkaline degrading agents disclosed are ammonium borate and alkali metal borates. Among the acidic degrading agents named are boric acid and inorganic acid salts.
The use of cold water soluble polyvinyl alcohol in the absence of other resins or polymers as such bonding agent for disposable nonwoven fabrics, is disclosed in U.S. Pat. Nos. 3,654,928; 3,689,314; 3,692,725; and 3,808,165. To prevent premature structural weakening or disintegration of the fabric as a result of dissolution of the polyvinyl alcohol binder in the presence of body discharge fluids the polyvinyl alcohol film is oversprayed with a gelling or insolubilizing agent such as borax or a mixture reacting to form alkali metal borate in situ. The borax or alkaline borate is stated to react with the polyvinyl alcohol and cross-link at least the exposed surface areas to a sufficient degree to render the reacted binder, when dried, somewhat water resistant. When the treated fabric is exposed to a large excess of water, the borax is said to be leached out and thus enough of the cross-linkages in the polymer are destroyed to reduce water resistance to a non-effective level.